1. Field of the Invention
The present invention relates to an ester compound which can mainly be used as an epoxy resin curing agent affording a cured article having low dielectric constant, low moisture absorption and sufficient heat resistance, and an epoxy resin composition using the same. The ester compound and epoxy resin composition are particularly suitable for electric/electronic applications to cope with high frequency, such as resin for laminate, resin for sealing IC, etc., and are also used as molding materials, coating materials, adhesive materials, civil engineering and construction materials and the like.
2. Description of the Related Art
As materials for printed circuit board among epoxy resins used for electric/electronic applications, a combination of a bisphenol type epoxy resin and dicyandiamide has mainly been used, heretofore. With the recent realization of thin volume and multi-layer construction of the printed circuit board, low dielectric constant of the resin is required for the purpose of improving a signal velocity and impedance-matching of a circuit. Also, with the recent realization of high frequency of the signal, low dielectric dissipation factor of the resin for the purpose of reducing transmission loss of the signal is required.
A method of using a conventional epoxy resin in combination with a thermoplastic resin having low dielectric constant and low dielectric dissipation factor is suggested. Examples thereof include method of modifying with a reactive polybutadiene resin, method of dispersing powders of a polytetrafluoroethylene resin and the like.
Recently, transfer molding of an epoxy resin composition, which is economically useful, has been conducted for sealing semiconductors such as LSI, IC, transistor and the like. Particularly, surface-mounted packaging of LSI is conducted and there has been increased a case where LSI is directly immersed in a solder bath. In that case, since the resin-sealed package is exposed to high temperature of not less than 200.degree. C., water adsorbed in the resin-sealed package expands to cause a problem that a crack is formed in a sealing package for semiconductor.
Therefore, an improvement in low moisture absorption and low crack resistance is required to an epoxy resin sealing material. At present, glycidyl ether of o-cresol novolak is mainly used as the epoxy resin and a sealing material containing phenol novolak is mainly used as a curing agent. However, the above problems arise when the resin-sealed package absorbs moisture during the preservation so that it is practically used after moisture-proof packaging to avoid the problems. In order to solve these problems, a low-viscosity epoxy resin capable of charging a filler in high density, e.g. glycidyl ether epoxy resin having a tetramethylbiphenyl skeleton, have been developed for the purpose of obtaining low water absorption and is practically used. An epoxy resin wherein the moisture resistance is obtained by having a hydrophobic skeleton of dicyclopentadiene-phenol addition polymer, alkylene phenol, etc. is also developed.
However, these conventional techniques have the following problem. That is, the proportion of a thermoplastic resin to be used in combination becomes large so as to accomplish the desired dielectric constant because the dielectric constant of the epoxy resin as the base of the material for printed circuit board is high. Therefore, the heat resistance, adhesion properties, dimensional stability, chemical resistance, etc., as a feature of the epoxy resin, are deteriorated.
A current resin for sealing material, e.g. sealing material containing glycidyl ether of o-cresol novolak as a main component, is well-balanced in view of the heat resistance and moldability, but is inferior to a biphenyl type epoxy as a sealing resin for surface-mounted packaging. The biphenyl type epoxy has low moisture absorption and shows excellent physical properties as the sealing material for surface packaging. However, the heat resistance is inferior and a package crack is formed under high moisture absorption condition and, therefore, physical properties thereof are still to be insufficient. In case of an epoxy having a hydrophobic skeleton, there is a problem that the heat resistance is inferior because a distance between crosslinking points becomes long.
Therefore, desired now are an epoxy resin curing agent capable of producing a cured article having low dielectric constant, low dielectric dissipation factor and low moisture absorption without deteriorating the heat resistance, adhesion properties and workability of a conventional epoxy resin, and a composition thereof.